Study: Ancient humans 'altered' climate

An analysis of gases trapped in ice suggests levels of methane rose steadily around the Earth during the first millennium, scientists told the BBC. Much of the greenhouse gas came from huge fires lit by humans as they cleared land for settlements and farming.

Writing in the journal Science, the researchers said they analyzed traces of methane trapped in air bubbles within 2,000-year-old Antarctic ice.

They said much of the gas apparently came from the burning of biomass, such as wood or grass, rather than other known sources of methane including the burning of fossil fuels, or natural emissions of methane from swamps and wetlands.

"It shows that in pre-industrial times there were much higher levels of methane from wood and grassland fires than we ever thought before," lead researcher Dominic Ferretti, of the National Institute of Water and Atmospheric Research Limited in Wellington, New Zealand, told the BBC.

"The end result is that in the future, with climate change and inevitably warming, we are likely to experience more wild fires ... as it becomes warmer and drier."

Copyright 2005 by United Press International